It is well established that protective immunity against malaria can be achieved in by immunization with irradiated sporozoites. In recent years it has become evident that this immunity involves the participation of antibodies, CD4+ and CD8+ T cells. Very recently, we have also demonstrated that gamma delta T cells, induced by sporozoite immunization, are capable of inhibiting liver stage development of malaria parasites. These sporozoite-induced immune mechanisms recognize different epitopes of the CS protein and of other antigens of sporozoites and liver stages of this parasite. In order to gain a better understanding of the molecular basis and precise role of these effector mechanisms of immunity, and with the aim of developing immunogens capable of inducing these immune responses, we propose to investigate: 1. Induction of CD4+ T cell mediated immunity against exo-erythrocytic stages of P. yoelii and characterization of the CD4+ T cell sub-sets involved in protection. Through the use of synthetic constructs and live carriers, for immunization, we aim to define optimal conditions for the induction of CD4+ T cells capable of inhibiting the development of malaria liver stages. The characterization of the CD4+ T cell sub-set(s) involved in protection, should contribute significantly to the elucidation of the cellular and molecular basis of this anti-parasite activity and guide the design of more effective immunogens. 2. Functional and molecular characterization of gamma delta T cells capable of inhibiting the development of exoerythrocytic stages of P. yoelii. Lymphocytes bearing the gamma delta-TCR are a relatively recently defined T cell sub-set; their functional role remains largely unknown. Using sporozoite-immunized alpha Beta T cell deficient mice, and methodology we have recently developed for the culture of Murine gamma delta T cells, we have derived three gamma delta T cell clones, one of which inhibits the development of liver stages of P. yoelii. Using these clones, and others currently being generated by us, we plan to characterize certain basic properties of gamma delta T cells, such as their specificity and mechanisms of their antigen recognition and their functional role as an effector mechanisms against malaria. We expect these investigations will help to define some basic aspects of anti-malaria immunity. We hope, they may also contribute to a better understanding of the immune response to other intracellular microbes.